Turbo HSDPA System

ABSTRACT

A method of power saving for a wireless transceiver (FIGS.  1  and  2 ) is disclosed. The transceiver has an active power mode ( 504 ) and a reduced power mode ( 510 ). The transceiver is operated in the reduced power mode ( 510 ) and monitors transmissions from a remote wireless transmitter while in the reduced power mode. The transceiver identifies a transmission from in the remote wireless transmitter by a transceiver identity included in the transmission (FIG.  6 , UE identification). The transceiver transitions to the active power mode ( 512 ) in response to identifying the transmission.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit, under 35 U.S.C. §119(e)(1), of U.S.Provisional Application No. 60/655,590 (TI-60022PS), filed Feb. 22,2005, and of U.S. Provisional Application No. 60/733,333 (TI-60022PS1),filed Nov. 3, 2005, and incorporated herein by this reference.

BACKGROUND OF THE INVENTION

The present embodiments relate to wireless communications systems and,more particularly, to the Long Term Evolution of High-Speed DownlinkPacket Access (HSDPA) for a wireless communication system.

Wireless communications are prevalent in business, personal and otherapplications, and as a result the technology for such communicationscontinues to advance in various areas. One such advancement includes theuse of spread spectrum communications, including that of code divisionmultiple access (CDMA) which includes wideband code division multipleaccess (WCDMA) cellular communications, in CDMA communications, userequipment (UE) (e.g. a hand held cellular phone, personal digitalassistant, or other) communicates with a base station, where typicallythe base station corresponds to a “cell.” CDMA communications are by wayof transmitting symbols from a transmitter to a receiver, and thesymbols are modulated using a spreading code which consists of a seriesof binary pulses. The code runs at a higher rate than the symbol rateand determines the actual transmission bandwidth. In the current,industry, each piece of CDMA signal transmitted according to this codeis said to be a “chips,” where each chip corresponds to an element inthe CDMA code. Thus, the chip frequency defines the rate of the CDMAcode. WCDMA includes alternative methods of data transfer, one beingfrequency division duplex (FDD) and another being time division duplex(TDD, where the uplink and downlink channels are asymmetric for FDD andsymmetric for TDD. Another wireless standard involves time divisionmultiple access (TDMA) apparatus, which also communicate symbols and areused by way of example in cellular systems. TDMA communications aretransmitted as a group of packets in a time period, where the timeperiod is divided into time slots so that multiple receivers may eachaccess meaningful information during a different part of that timeperiod. In other words, in a group of TDMA receivers, each receiver isdesignated a time slot in the time period, and that time slot repeatsfor each group of successive packets transmitted to the receiver.Accordingly, each receiver is able to identify the information intendedfor it by synchronizing to the group of packets and then deciphering thetime slot corresponding to the given receiver. Given the preceding, CDMAtransmissions are receiver-distinguished in response to codes, whileTDMA transmissions are receiver-distinguished in response to time slots.

Since CDMA and TDMA communications are along wireless media, then thetravel of those communications can be affected in many ways, andgenerally these effects are referred to as the channel effect on thecommunication. For example, consider a transmitter with a single antennatransmitting to a receiver with a single antenna. The transmitted signalis likely reflected by objects such as the ground, mountains, buildings,and other things that it contacts. In addition, there may be othersignals that interfere with the transmitted signal. Thus, when thetransmitted communication arrives at the receiver, it has been affectedby the channel effect. Consequently, the originally-transmitted data ismore difficult to decipher due to the added channel effect. Variousapproaches have been developed in an effort to reduce or remove thechannel effect from the received signal so that theoriginally-transmitted data is properly recognized. In other words,these approaches endeavor to improve signal-to-interference+noise ratio(SINR), thereby improving other data accuracy measures (e.g. bit errorrate (BER), frame error rate (FER), and symbol error rate (SER)).

One approach to improve SINR is referred to in the art as antennadiversity, which refers to using multiple antennas at the transmitter,receiver, or both. For example, in the prior art, a multiple-antennatransmitter is used to transmit the same data on each antenna where thedata is manipulated in some manner differently for each antenna. Oneexample of such an approach is space-time transmit diversity (“STTD”).In STTD, a first antenna transmits a block of two input symbols over acorresponding two symbol intervals in a first order while at the sametime a second antenna transmits, by way of example, the complexconjugates of the same block of two symbols and wherein those conjugatesare output in a reversed order relative to how they are transmitted bythe first antenna and the second symbol is a negative value relative toits value as an input.

Another approach to improve SINR combines antenna diversity with theneed for higher data rate. Specifically, a multiple-inputmultiple-output (MIMO) system with transmit diversity has been devised,where each transmit antenna transmits a distinct and respective datastream. In other words, in a MIMO system, each transmit antennatransmits symbols that are independent from the symbols transmitted byany other transmit antennas for the transmitter and, thus, there is noredundancy either along a single or with respect to multiple of thetransmit antennas. The advantage of a MIMO scheme using distinct andnon-redundant streams is that it can achieve higher data rates ascompared to a transmit diversity system.

Communication system performance demands in user equipment, however, areoften dictated by web access. Applications such as news, stock quotes,video, and music require substantially higher performance in downlinktransmission than in uplink transmission. Thus. MIMO system performancemay be further improved for High-Speed Downlink Packet Access (HSDPA) byOrthogonal Frequency Division Multiplex (OFDM) transmission. With OFDM,multiple symbols are transmitted on multiple carriers that are spacedapart to provide orthogonality. An OFDM modulator typically takes datasymbols into a serial-to-parallel converter, and the output of theserial-to-parallel converter is considered as frequency domain datasymbols. The frequency domain tones at either edge of the band may beset to zero and are called guard tones. These guard tones allow the OFDMsignal to fit into an appropriate spectral mask. Some of the frequencydomain tones are set to values which will be known at the receiver, andthese tones are termed pilot tones or symbols. These, pilot symbols canbe useful for channel estimation at the receiver. An inverse fastFourier transform (IFFT) converts the frequency domain data symbols intoa time domain waveform. The IFFT structure allows the frequency tones tobe orthogonal. A cyclic prefix is formed by copying the tall samplesfrom the lime domain waveform and appending them to the front of thewaveform. The time domain waveform with cyclic prefix is termed an OFDMsymbol, and this OFDM symbol may be upconverted to an RF frequency andtransmitted. An OFDM receiver may recover the timing and carrierfrequency and then process the received samples through a fast Fouriertransform (FFT). The cyclic prefix may be discarded and after the FFT,frequency domain information is recovered. The pilot symbols may berecovered to aid in channel estimation so that the data sent on thefrequency tones can be recovered. A parallel-to-serial converter isapplied, and the data is sent to the channel decoder. Just as withHSDPA, OFDM communications may be performed in an FDD mode or in a TDDmode.

While the preceding approaches provide steady improvements in wirelesscommunications, the present inventors recognize that still furtherimprovements may be made, including by addressing some of the drawbacksof the prior art. Examples of these improvements addressed byembodiments of the present invention include improved frequencydiversity to reduce inter-cell interference, improved power control, andimproved control information, indeed, to address some of these issues,the present inventors described in co-pending U.S. patent applicationSer. No. 10/230,003 (docket: TI-33494), filed Aug. 28, 2002, entitled.“MIMO HYBRID-ARQ USING BASIS HOPPING”, and hereby incorporated herein byreference. In this referenced application, multiple independent streamsof data are adaptively transmitted with a variable basis selected toimprove signal quality. Further, a receiver is provided that decodes thetransmitted signals including the multipaths therein. While thisimprovement therefore provides various benefits as discussed in thereferenced application, the inventors also recognize still additionalbenefits that may be achieved with such systems. Accordingly, thepreferred embodiments described below are directed toward these benefitsas well as improving upon the prior art.

BRIEF SUMMARY OF THE INVENTION

In a first preferred embodiment, a transceiver saves power during atransmit time interval. The transmit time interval includes a pluralityof OFDM symbols transmitted sequentially in time. The transceiverreceives a first OFDM symbol in the transmit time interval in an activepower mode. The transceiver determines if there are other OFDM symbolsfrom the plurality of OFDM symbols for the transceiver in response tothe control and pilot channels within the first OFDM symbol. Thetransceiver operates in the active power mode for the remainder of thetransmit time interval if there are other OFDM symbols for thetransceiver. The transceiver operates in a reduced power mode for aremainder of the transmit time interval if there are no other OFDMsymbols for the transceiver.

In a second preferred embodiment, the transmitter forms a plurality ofsymbols in a packet with pilot and control signals in a first symbol ofthe plurality of symbols. Pilot signals are excluded from at leastanother symbol of the plurality of symbols. The packet is thentransmitted to remote user equipment (UE).

According to a third preferred embodiment, the transmitter transmits aplurality of orthogonal frequency division multiplex (OFDM) controlchannels during a transmit time interval. The control channels may havedifferent structures as defined by their size and correspondingmodulation and coding scheme. The transmitter also transmits a counterduring the transmit time interval to indicate a number of controlchannels for each structure in the transmit time interval.

According to a fourth preferred embodiment, the transmitter transmits aplurality of orthogonal frequency division multiplex (OFDM) controlchannels during a transmit time interval. The transmitter also transmitsa counter to indicate a data block size associated with each controlchannel during the transmit time interval.

In a fifth preferred embodiment, the transmitter transmits a broadcastorthogonal frequency division multiplex (OFDM) signal over a pluralityof broadcast channels during a transmit time interval. The transmitteralso transmits a broadcast channel bitmap to indicate which channels areactive.

According to a sixth preferred embodiment, a transceiver operates in anactive power mode and in a reduced power mode during a communicationssession. The transceiver transitions to the active power mode only atpredefined time intervals of the communications session. The transceiveroperates at the reduced power mode for the remainder of thecommunications session. This may be useful and applicable for a servicesuch as voice over internet protocol (VoIP) in which there may beperiodic communication of small packets, and the control overhead can bereduced by scheduling the transmission intervals in advance. Moreover,the UE needs to monitor transmissions only at predetermined timeintervals thereby conserving power for the remainder of thecommunications session by reverting to the reduced power mode.

Other devices, systems, and methods are also disclosed and claimed.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a block diagram of a transmitter that may employ embodimentsof the present invention;

FIG. 2 is a block diagram of a receiver that may employ embodiments ofthe present invention;

FIG. 3 illustrates multiplexed frequency allocation units of thetransmitter of FIG. 1;

FIG. 4 illustrates organization of pilot, data, and control signals ofan OFDM symbol of FIG. 3;

FIG. 5 is a state diagram of power control modes of the presentinvention;

FIG. 6 illustrates the structure of an OFDM shared control channel(SCOT) according to the present invention; and

FIG. 7 illustrates the structure of an OFDM broadcast/multicast (BCMCS)shared control channel (SCCH).

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiments of the present invention provide interferencereduction and power savings for a wireless communication system. Thewireless communication system preferably provides for the Long TermEvolution of High-Speed Downlink Packet Access (HSDPA) andmultiple-input multiple-output (MIMO) as will be explained in detail. Asimplified block diagram of a wireless transmitter of the presentinvention for such a system is shown in FIG. 1. The wireless transmitterreceives a data stream at input 100 from a baseband processor (notshown). This data stream may include pilot signals, control signals, anddata signals for synchronization and control of remote wireless userequipment (UE). The data is encoded, interleaved, and modulated bycircuit 102 and applied to the multiple antenna processing circuit 104.The multiple antenna processing circuit 104 can provide for spatialmultiplexing or transmit diversity and performs other functions as willbe described in detail. Per antenna rate control (PARC) may be performedby having multiple blocks 102 (not shown) in order to have differentmodulation and/or coding on each antenna stream. Transmit diversity mayinclude open loop or closed loop modes or a combination of open andclosed loop modes. Open loop modes may include STTD, which was describedearlier. Closed loop modes may include transmit adaptive array (TxAA),which is a form of beamforming. In addition, double STTD or TxAA may beused with four antenna transmission when a trade-oil between diversitygain and spatial multiplexing is desired. The output of multiple antennaprocessing circuit 104 is then applied to the OFDM modulation circuits106 and transmitted by transmit antennas 108. Preferred embodiments ofthe present invention may include one, two, four, or more transmitantennas 108. Thus. OFDM modulation circuits 106 receive multiple inputsmid produce multiple outputs.

Referring to FIG. 2, there is a simplified block diagram of a wirelessreceiver of the present invention, inventive features of the transmitterof FIG. 1 are included in the receiver for compatibility. Antennas 200receive signals from a remote transmitter as in FIG. 1. In a preferredembodiment, there are 1, two, four, or more antennas 200. Signals fromantennas 200 are applied to OFDM demodulator circuit 202. The output ofOFDM demodulator circuit 202 is applied to circuit 208 to extract pilotsignals that are used to synchronize the receiver with the remotetransmitter. These pilot signals may have a power boost relative to datasignals. The extracted pilot signals are applied to circuit 210 tocompute the effective channel between the receiver and remotetransmitter. The outputs of OFDM demodulator circuit 202 are applied tothe multi-antenna processing circuit 204 and corrected by the effectivechannel estimate from circuit 210. Different types of multi-antennaprocessing can be used such as linear, decision feedback, or maximumlikelihood. These signals are subsequently converted to a serial datastream as will be explained with reference to FIG. 3. The serial datastream is then demodulated and, decoded in circuit 206, and applied to abaseband processor. An optional feedback loop 212 from circuit 206 tocircuit 204 allows a decision feedback operation which can improve theestimation of data bits.

Referring now to FIG. 3, there is a diagram showing the exemplarystructure of an HSDPA packet produced by multi-antenna processingcircuit 104 of FIG. 1. For the purpose of illustration, there are fiveseparate packets in the diagram of FIG. 3. In this exemplary embodimenteach packet includes three OFDM symbols shown in columns. However, thepacket may comprise a different number of OFDM symbols. The first OFDMsymbol includes a shared control channel (SCOT) aid common pilot channelmultiplexed with data. For example, the first packet includes (OFDMsymbols 300, 302, and 304. The second packet includes OFDM symbols 306,308, and 310. Each group of three OFDM symbols is transmitted in arespective transmit time interval (TIT). For the purpose ofillustration, each TTI has duration of 0.5 milliseconds. Each OFDMsymbol includes eight sub-bands. These sub-bands provide frequencydiversity within each OFDM symbol of the wireless communication system.According to the present invention the order of these sub-bands in thefirst OFDM symbol, for example symbol 300, is randomly selected. Theorder of sub-bands in each remaining OFDM symbol is obtained by a cyclicshift of the order of the first OFDM symbol. For example, sub-bands ofOFDM symbol 302 are shifted five positions so that the position ofsub-band 8 in OFDM symbol 302 corresponds to the position of sub-band 3in OFDM symbol 300. Sub-bands of OFDM symbol 304 are shifted anotherfive positions so that the position of sub-band 8 in OFDM symbol 304corresponds to the position of sub-band 6 in OFDM symbol 300. Addedfrequency diversity of this sub-band packet structure advantageouslyreduces inter-cell interference by averaging the interference overdifferent sub-bands. This increases the SINR within the cell and isparticularly improves communication at high Doppler rates.

Recall from the discussion of FIG. 3 that the first OFDM symbol of eachpacket includes a shared control channel (SCCH) and common pilot channelmultiplexed with data. By way of example, the diagram of FIG. 4illustrates individual tones or discrete frequencies that modulate thesub-bands for the first OFDM symbol in each packet for the case of twotransmit antennas. Substantially all pilot signals and control signalsare included in the first OFDM symbol, of each packet. Alternatively,for a four antenna system, a similar structure may be necessary for thefirst two OFDM symbols of each packet. Preferably at least one or moresubsequent OFDM symbols in the packet would be reserved for data signalsnot including pilot signals or control signals. For example, pilotsignals 400-406 in the first OFDM symbol 300 (FIG. 3) are transmittedfrom a first antenna. Pilot signals 410-416 in the first OFDM symbol 300are transmitted from a second antenna. This organization of pilot andcontrol signals advantageously promotes rapid synchronization of userequipment (UE) in a cell with a base station. Each UE may monitorcontrol signals and determine whether a particular packet includes anydata for that UE. When a particular UE determines that the packet doesnot include relevant data, the UE may enter a low power mode ofoperation for the remainder of the transmit time interval (TTI). Forexample, with the packet structure of FIG. 3, each UE would monitor afirst OFDM symbol 300 in a first packet. Each UE in the cell that foundits UE identity in the control information would continue to monitor theremaining OFDM symbols 302 and 304 to process relevant data. However,any UE that did not detect its UE identity in the control informationwould enter a low power state for the remaining TTI. Thus, significantpower is conserved by each UE in the cell when no relevant data isincluded in packets.

Because there are a limited number of tones available in the first OFDMsymbol, the shared control channel may be split into two parts. In oneembodiment, the UE identities may be transmitted as part of the sharedcontrol channel in a common part and transmitted in the first OFDMsymbol. The UE dedicated scheduling information, may be transmitted in adedicated part of the shared control channel and transmitted in thefirst and second OFDM symbols or, alternatively, throughout the TTI. UEdedicated scheduling information may contain information related to theHybrid-ARQ process, the modulation and coding scheme, the transportformat, or other features. This split of the SCCH into common anddedicated parts allows the UE to save power. The common and dedicatedparts of the SCCH preferably have different code rates. The UE maymonitor the first OFDM symbol. If the UE identity is not contained inthe first OFDM symbol, the UE does not need to process the rest of theOFDM symbols in the TTI. With reference to FIG. 3, for example, the UEidentities may be contained in the control channel transmitted in thefirst OFDM symbol 300, while the remainder of the shared control channelmay be transmitted in OFDM symbols 300 and/or 302.

The foregoing discussion with regard to FIGS. 3 and 4 is by way ofexample only. For example, power saving advantages of the presentinvention will be even greater for more OFDM symbols in each TTI. Alonger TTI would permit each UE to enter a reduced power mode forgreater periods of time, thereby conserving even more power when apacket contained no relevant data. However, additional pilot signals maybe necessary for any UE that does receive relevant data during the TTI.These additional pilot signals may be included in at least another OFDMsymbol within the longer TTI so that circuits 208 and 210 (FIG. 2) mayupdate the channel estimate.

Given the above. FIG. 5 illustrates three operational modes of a typicalUE in the cell. Active mode 504 is a normal operational mode in whichthe UE transmits and receives data. When, the UE does not receive atransmission for a first predetermined time after a most recenttransmission from the base station, it transitions to a power savingmode 510 as shown by path 508. If the UE still does not receive atransmission for a second predetermined time after a most recenttransmission from the base station, it transitions to a sleep mode 500as shown by path 514. The sleep mode 500 produces an even greater powersavings than the power saving mode 510. However, the UE must thenreceive a page from the base station to power up and return to theactive mode 504 along path 502. Alternatively, if the UE receives avalid transmission over the SCCH while in the power saving mode 510before elapse of the second predetermined time, it returns to activemode 504 along path 512. Furthermore, from active mode 504, the UE mayalso receive a sleep instruction and move directly to sleep mode 500 asillustrated by path 506, in this manner, each EU in the cell conservessignificant power but remains responsive to subsequent packettransmissions.

In an alternative embodiment of FIG. 5, the UE transitions from activemode 504 to power saving mode 510 as shown by path 508 for apredetermined time after it receives a transmission. This predeterminedtime is preferably an integral number of transmit time intervals. Afterthis predetermined time, the UE transitions back to the active mode 504along path 512. This embodiment of the present invention advantageouslyreduces control signal overhead between the base station and the UE andmaintains the power saving features of the previous embodiment.

In an embodiment of the present invention, the base station transmits acounter during each TTI to indicate a number of shared control channels(SCCH) in the TIT. There is generally one SCCH for each UE. The UEdepends on a UE identification field in the OFDM SCCH foridentification. The counter may have several values. Each value isassociated with a particular shared control channel size. For example, afirst counter value of two may indicate two shared control channels of afirst size. A second counter value of three may indicate three sharedcontrol channels of a second size, in another embodiment of the presentinvention the base station transmits a power control counter during eachTTI to indicate a number of power control bits in the TTI.

In another embodiment of the present invention, the base stationtransmits a block size designator during each TTI. The block sizedesignator advantageously provides flexible block sizes to accommodate avariable number of shared control channels and other control informationin each TTI.

Turning now to FIG. 6, there is a diagram of the OFDM SCCH structureillustrating features of the present invention. The diagram identifieseach particular control feature of the SCCH in the left column.Corresponding control bits associated with each control feature aregiven in the right column. For example, multiple power control bits aretransmitted during each TTI on the OFDM transmit power control channel(TPCCH). A modulation scheme is transmitted in 7 bits during the TTI.The modulation scheme preferably identifies the modulation format andantenna grouping. For example, the modulation formats may includequadrature phase shift keying (QPSK), 16-quadrature amplitude modulation(16-QAM), or 64-quadrature amplitude modulation (64-QAM). The selectedmodulation format would typically depend on signal quality and desireddata rate. Moreover, the modulation format may be different for eachantenna and each LIE. The block size identifier designates the variableblock size within the TTI. The Hybrid-ARQ field identifies the automaticrepeat request (ARQ) format to each UE. In response to a transmissionfrom the base station, the UE will acknowledge (ACK) or not acknowledge(MACK; receipt of the transmission. The UE identification fieldidentifies the SCCH corresponding to a specific UE as previouslydiscussed.

Referring now to FIG. 7, there is a diagram of a broadcast/multicast(BCMCS) SCCH structure illustrating features of the present invention.As with FIG. 6, the diagram identifies each particular control featureof the SCCH in the left column. Corresponding control bits associatedwith each control feature are given in the right column. However, thebroadcast channels are generally only monitored by the UE much as onemight watch television. Thus, several control features such asHybrid-ARQ, Redundancy, New-data indicator, and UE identification areunnecessary. Furthermore, no power control bits are transmitted in theBCMCS slots and each BCMCS transmit time interval (TTI) is preferably1.0 millisecond. According to the present invention, the base stationtransmits a bitmap in each TTI to indicate which BCMCS data streams areactive. For example, if the BCMCS accommodates a maximum of 12 datastreams, a 12-bit bit map is transmitted during each TTI. A value of 0indicates a data stream is inactive, and a value of 1 indicates the datastream is active. Thus, the LIE may check the bitmap to determine whichdata stream to monitor. This advantageously eliminates a need to monitorall data streams of the BCMCS. Moreover, the UE may also identify whichBCMCS shared control channels (SCCH) to ignore. This is because theshared control channels are transmitted sequentially and correspond tothe order of the bitmap.

Still further, while numerous examples have thus been provided, oneskilled in the art should recognize that various modifications,substitutions, or alterations may be made to the described embodimentswhile still tailing with the inventive scope as defined by the followingclaims.

1-9. (canceled)
 10. A method of transmitting an orthogonal frequencydivision multiplex (OFDM) signal, comprising the steps of: transmittingon a plurality of control channels during a transmit time interval; andtransmitting a counter during the transmit time interval to indicate anumber of the plurality of control channels in the transmit timeinterval.
 11. A method as in claim 10, wherein each control channelcorresponds to a respective user in a wireless cell.
 12. A method as inclaim 10, wherein the counter value specifies a number of the pluralityof control channels with a specific coding and modulation scheme.
 13. Amethod of transmitting an orthogonal frequency division multiplex (OFDM)signal during a transmit time interval (TTI), comprising the steps of:transmitting a plurality of control channels during a transmit timeinterval, each control channel corresponding to a respective user; andtransmitting a counter associated with each respective control channelto indicate a size of said each respective control channel of theplurality of control channels.
 14. A method as in claim 13, wherein thesize of said each respective control channel is variable.
 15. A methodof transmitting a broadcast orthogonal frequency division multiplex(OFDM) signal, comprising the steps of: determining a plurality ofbroadcast channels; transmitting on a set of broadcast channels withinthe plurality of broadcast channels during a transmit time interval(TTI); and transmitting a broadcast channel bitmap to indicate the setof broadcast channels are active during the transmit time interval. 16.A method as in claim 15, wherein a number of the set of broadcastchannels is less than a number of the plurality of broadcast channels.17. A method as in claim 15, wherein broadcast channels of the pluralityof broadcast channels other than the set of broadcast channels areinactive during the transmit time interval. 18-23. (canceled)
 24. Amethod of transmitting a control channel, comprising the steps of:transmitting a first part of the control channel that is encoded; andtransmitting a second part of the control channel that is encodeddifferently than the first part.
 25. A method as in claim 24, whereinthe control channel is an orthogonal frequency division multiplex (OFDM)control channel.
 26. A method as in claim 24, wherein the first part isa common part comprising user equipment (UE) identities, and wherein thesecond part is a UE dedicated part.